Spain's Constitutional Court has suspended next Monday's session of Catalan parliament, in a bid to pre-empt a possible push for independence.
The court said such a move would be "a breach of the constitution".
Earlier Prime Minister Mariano Rajoy warned Catalonia's regional government against declaring independence after a disputed vote last Sunday.
Catalan leader Carles Puigdemont had indicated that he could make such a declaration at next week's session.
The court's ruling on Thursday upheld a challenge by Catalonia's Socialist Party, which opposes secession from Spain, and not from the government in Madrid.
Allowing the regional parliament to meet and declare independence, the court said, would violate the rights of the party's MPs.
An earlier ruling by the court aimed at stopping Sunday's vote was ignored by Catalonia's leaders. That challenge to the court had come from Spain's government, which condemned the referendum as illegal.
Organisers of Sunday's vote put the turnout at 42%, with 2.2 million people taking part. They say 90% voted for independence, however they have not published final results. There have been several claims of irregularities.
There was violence at polling stations as police, trying to enforce a Spanish court decision to ban the vote, attempted to seize ballot boxes and disperse voters.